Power Station Planner

What turns the generator?

Almost every power station does the same job in the end: it turns a generator. Inside, a magnet spins near coils of wire, and that makes a voltage. What differs is what does the turning. Most stations boil water and let the steam push a turbine round. Some let the wind or moving water push it directly. Planning a supply means asking two questions of every resource: will it run out, and can it run when the town needs it?

Words for planning a supply

Five terms for every question about generating electricity.

Which will not run out?

Select the FOUR resources that are renewable.

• Wind
• The tides
• Biofuel
• Light from the Sun
• Coal
• Natural gas
• Nuclear fuel

Two ways to turn a turbine

Every resource below reaches the generator by one of two routes. Solar cells are the odd one out: they make a voltage straight from light, with no turbine or generator at all.

From fuel to voltage

Put the stages inside a gas-fired steam power station in order.

• Gas is burned in the boiler
• Water in the pipes boils
• High-pressure steam rushes through the turbine
• The turbine shaft spins the magnet in the generator
• A voltage is produced across the coils of wire

What turns the turbine here?

The turbine jams

In a coal-fired station the turbine jams and stops, although the boiler is still full of hot steam. What happens to the electricity output?

• It falls to zero, because the magnet is no longer moving near the coils
• It stays the same, because the steam is still hot
• It halves, because only the steam side is still working
• It rises, because more energy builds up in the steam

Judge it by when it can run

An exam answer that just lists pros and cons earns little. The better question is whether a resource can deliver when the demand is there. Wind turbines turn only when the wind blows, and solar cells give out nothing after dark. The tides are predictable, but the output still rises and falls through the day. Stations that burn fuel can run whenever fuel is supplied, and gas-fired ones can be brought up to full power quickly. A nuclear station runs steadily for months but is slow to change its output. A hydroelectric dam can start within minutes, as long as its reservoir holds water.

Calm, dark and cold

It is a still winter evening, and demand is about to jump as people get home. Which of these can a planner switch on and rely on in the next hour?

• The gas-fired station
• The wind farm
• The solar farm
• A second nuclear station that is currently switched off

Plot the town day

This is an invented example town. Its demand at hours 0, 4, 12 and 24 is already plotted. Plot the other three readings: 70 MW at hour 8, 70 MW at hour 16 and 90 MW at hour 20.

Cover the evening peak

On the graph you plotted, demand never falls below 30 MW and peaks at 90 MW in the evening. A nuclear station supplies a steady 30 MW all day and night. How many megawatts must quick-start stations supply at the evening peak?

Two answers, one wins

Asked whether a solar farm could supply the town, one student wrote that solar is clean but unreliable. That is true of every solar farm, so it shows nothing about this one. A second student wrote that the solar farm gives nothing after dark, but the town needs its most power, 90 MW, at hour 20, so solar cannot cover the peak without another source. That answer uses the figures in front of it, which is what the marks are for.

Find the data-led sentences

A table shows a wind farm gave 15 MW on four days of one week and nothing on the other three, which were calm. A student wrote five sentences about it. Tap the TWO that use the data given.

• Wind power is renewable and good for the planet.
• On three calm days of the seven, it gave nothing at all.
• Some people think wind farms spoil the view.
• Even on its good days, its 15 MW is far below the 90 MW evening peak.
• The wind is free, so it must be the cheapest choice.

Plan the supply

Use what you know about each resource, and the facts given, to make each decision.

• A small island has strong winds most of the year, no gas supply, and batteries that can cover a few calm hours. Which main source fits?
• Demand in a city jumps every weekday evening for about two hours, then falls back. What should meet the jump?
• A country wants a large, steady supply all year that releases very little carbon dioxide, and it has a safe store for long-lived waste. Which fits best?
• A table of a coastal scheme shows its output peaking and stopping twice a day, on a timetable that can be worked out years ahead. Which resource is it using?

Plan the town supply

The town from your graph needs at least 30 MW all day and 90 MW at its evening peak. Plan a mix of power stations to supply it, and justify each choice using the figures and what you know about each resource.

• Which resource covers the steady 30 MW, and why it suits that job
• What meets the rise to the evening peak, and how fast it must start
• Where a renewable fits, and when it may not be available
• One environmental cost of your plan